The invention relates to biocontrol agents for suppressing weed growth. More specifically the present invention relates to bacterial biocontrol agents for suppression of weed growth.
Control of weeds is an important aspect of crop management. Due to several undesirable properties associated with the use of chemical herbicides, alternative weed control practices, including the use of biological herbicides, are desired. For example, rising economic, environmental and social costs associated with agricultural inputs, spray drift, pesticide residues, government legislation for reduced pesticide use, along with the development of herbicide resistance in weeds, make biocontrol agents attractive strategies for weed control.
Biological control of weeds with microorganisms (bioherbicides), preferably involves the production and application of a weed-specific pathogen to a target weed. The weed specific pathogen is typically a fungus or bacterial pathogen that inhibits or suppresses root, shoot or both root and shoot growth, development, or both growth and development, thereby reducing weed competition. The development of biological crop protection products (bioherbicides) for economically important weed problems in agricultural field crops may help to facilitate harvests, secure yields, and protect the environment. Biological control provides an additional tool to complement an integrated weed management system and helps sustainable agricultural systems by maintaining the ecosystem balance through the preservation of plant and microbial diversity in the field.
An important aspect in the development of a successful biological control agent is an effective delivery system which can be readily integrated into existing farming practices and commercial production. Rhizobacteria (root-colonizing bacteria) being developed as bioherbicides have been encapsulated into sodium alginate granules and shown to be a suitable method for survival and distribution of microbial inocula in the soil environment (Hall, B. M., A. J. McLoughlin, K. T. Leung, J. T. Trevors and H. Lee 1998. Transport and survival of alginate-encapsulated and free lux-lac marked Pseudomonas aeruginosa UG2Lr cells in soil. FEMS Microbiol. Ecol. 26:51-61.; and Mooney, H. D., S. M. Boyetchko, and Z. K. Punja. 1996. Development of application techniques for biological weed control using rhizobacteria. p. 297-299 in IX International Symposium on Biological Control of Weeds, Stellenbosch, South Africa.). Another method of encapsulation is the ‘Pesta’ process (Connick, W. J. Jr., C. D. Boyette and J. R. McAlpine 1991. Formulation of mycoherbicides using a pasta-like process. Biol Control 1:281-287.), which has been shown to extend the shelf-life of a dried encapsulated bioherbicide (Connick, W. J. Jr., D. Daigle, K. Williams, B. Vinyard, D. Boyette and P. J. Quimby Jr. 1996. Shelf life of a bioherbicide product. Am. Biotechnol. Lab. 14:34-37.; Connick, W. J. Jr., D. J. Daigle, C. D. Boyette, K. S. Williams, B. T. Vinyard and P. C. Quimby Jr. 1996. Water activity and other factors that affect the viability of Colletotrichum truncatum conidia in wheat flour-kaolin granules ('Pesta). Biocontrol Sci. Technol. 6:277-284.; and Connick, W. J. Jr., D. J. Daigle, A. B. Pepperman K. P. Hebbar, R. D. Lumsden, T. W. Anderson and D. C. Sands 1998. Preparation of stable, granular formulations containing Fusarium oxysporum pathogenic to narcotic plants. Biol Control 13:79-84.).
There are several documents disclosing the use of fungi as biocontrol agents. For example, U.S. Pat. No. 5,993,802 teaches methods for suppressing the growth of Calamagrostis canadensis using an isolate of a low temperature basidiomycete fungus, Coprinus psychromorbidus. U.S. Pat. No. 5,472,690 teaches of a mycoherbicide (including at least one or both of Fusarium nivalis and Colletotrichum calamagrostidis) effective in the control of Calamagrostis canadensis and/or related grasses. The control of crabgrass using fungi is disclosed in U.S. Pat. No. 5,952,264, using the fungus Cochliobolus intermedius, and U.S. Pat. No. 5,635,444 using a fungus selected from the genus Curvularia. U.S. Pat. No. 5,747,029, teaches the control of sicklepod weeds using the fungus Myrothecium verrucaria. The control of nutsedge weeds using the fungus Dactylaria higginsii is disclosed in WO 98/08389. U.S. Pat. No. 4,606,751 teaches the biocontrol of Johnson grass using Bipolaris sorghicola spores that are suspended in a solution of water and surfactant, and sprayed onto a field in which the weed is growing.
U.S. Pat. No. 6,022,828 discloses the use of a Xanthomonas campestris pathovar (a bacteria) as a bioherbicide for controlling Poa trivialis. Strains of Drechslera monoceras which show herbicidal effects against all varieties of barnyard grass, for example Echinochloa spp is taught in U.S. Pat. No. 5,498,591. Modified and unmodified soil and rhizo-plane bacterial strains, specifically Pseudomonas putida strain (FH160), useful for the control of weeds such as downy brome, Japanese brome and jointed goatgrass in the vicinity of wheat is presented in U.S. Pat. No. 5,332,673. U.S. Pat. No. 5,332,573 discloses the use of strains of Drechslera which possess herbicidal effects against all varieties of barnyard grass such as Echinochloa. U.S. Pat. Nos. 5,192,541 and 5,077,045 both teach the control of weed grasses by infecting them with a Xanthomonas campestris pathovar. U.S. Pat. No. 5,030,562 discloses the use of non-fluorescent Pseudomonas strains which inhibit downy brome. Japanese Patent 10179139 teaches Drechslera monoceras having selected herbicidal activities against Echinochloa. European Patent EP 839,449 discloses a herbicide containing phytopathogenic microorganisms such as Drechslera or Exserohilum.
The combination treatment of applying a chemical such as a herbicide (glyphosate) and a bacterial plant pathogen (Pseudomonas synringae pv. tabaci) for controlling the growth of weeds is disclosed in WO 91/03161. The use of genetically modified Pseudomonas strains that have enhanced biocontrol properties against fungi such as Rhizoctonia and Pythium is taught in U.S. Pat. No. 5,955,348.
Annual grassy weeds such as Setaria viridis (L.) Beauv. (commonly known as green foxtail, pigeongrass, wild millet, green bristlegrass, and bottlegrass) and Avena fatua (L.) (commonly known as wild oat) develop dense competitive stands and have heavy seed production in spring sown crops. Green foxtail is a principal weed of corn, soybean, cereals, flax, canola, sugar beets, and pastures. Wild oat is considered to be one of the three most serious weed problems in cereal production areas. The amount of damage to the crop depends on the density of the stand, time of emergence, and length of time the weed and crop are competing. Weed surveys for herbicide-resistant wild oat and green foxtail have revealed that there is a high incidence of group-1 herbicide-resistant wild oat populations (48% of fields surveyed) and 28% had either group-1 or group-3 herbicide-resistant green foxtail populations (Beckie, H. J., A. Legere, A. G. Thomas, L. T. Juras, and M. D. Devine. 1996 Survey of Herbicide-Resistant Wild Oat and Green Foxtail in Saskatchewan: Interim Report. AAFC Report, 22 pp.). Therefore, biocontrol of these and other plants, for example, foxtail barley (Hordeum jubatum), crabgrass (Digitaria sanguinalis), annual ryegrass (Lolium rigidum), barnyard grass (Echinochloa crusgalli), yellow foxtail (Setaria glauca), Italian rye grass (Lolium multiflorum), Goose grass (Eleusine indica), green foxtail (Setaria viridis), and wild oat (Avena fatua) is highly desirable. However, for most of these weeds there are no known biocontrol agents.